Conversion of polyalkyl aromatics to monoalkyl aromatics



Patented Oct. 31, 1950 UNITED STATES CONVERSION OF POLYALKYL AROMATICS TO MONOALKYL AROMATICS George N. (Jade, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application January 2, 1948, Serial N6. 126

3 Claims.

This invention relates to the manufacture of gasoline. In another aspect this invention relates to a process for the manufacture of premium gasoline stocks from cracking. In a more specific aspect this invention relates to a process for obtaining improved yields and quality of gasoline product from cracking hydrocarbon oils.

This invention has for an object to provide a process for the manufacture of gasoline stocks.

Another object is to provide a process for the manufacture of premium gasoline stocks in improved yield and quality from hydrocarbon cracking products.

Another object is to provide a process for the utilization of a spent ca alyst previously used for removing organically combined fluorine from hydrocarbons.

Still another object of this invention is to provide a process for the manufacture of monoalkyl aromatic hydrocarbons from a fraction rich in polyalkyl aromatics.

Other objects and advantages will be apparent to one skilled in the art from the accompanying discussion and disclosure.

This invention provides a novel and unitary combination process for increasing the yield and quality of gasoline obtained by cracking. Briefly, a preferred embodiment of the invention may be summarized as follows:

1. A cracked hydrocarbon oil is fractionated to obtain a light gasoline fraction, a heavy gasoline fraction, and an aromatic naphtha fraction.

2. The heavy gasoline fraction is treated with isobutane and hydrofluoric acid under alkylation conditions to obtain a substantially non-olefinic gasoline fraction containing branched-chain octanes, which is defluorinated with bauxite and reblended with the light gasoline fraction.

3. The aromatic naphtha is mixed with benzene and contacted with bauxite that has been used in the defiuorination mentioned above. The product is a fraction containing monoalkylated aromatics boiling in the gasoline range. It is blended with the light gasoline fraction and the heavy alkylated gasoline fraction mentioned above.

A more detailed explanation will be given with reference to the attached drawing.

A cracking stock, e. g. a topped crude, enters cracking zone 2 through inlet I. Cracking zone 2 may be a conventional thermal or a catalytic cracking system; in many cases, it will be a thermal cracking unit and may be considered so here for illustration purposes. It may be operated at about 800 to 950 F. and about 300 to 800 p. s. i., specific conditions depending on the feed used and the degree of conversion desired. When catalytic cracking is used, the feed oil is vaporized, diluted with steam, and heated to about 850-l100 F. The vaporized and diluted oil is then contacted with a catalyst at about 0-100 p. s. i. and a liquid space velocity of about 1 to 10 volumes of oil per volume of catalyst per hour. Suitable catalysts are mixtures comprising silica and alumina, acid-treated clays, and alumina promoted with minor proportions of oxides of elements of groups V and VI of the periodic table. The exact conditions used will depend on the type of oil to be cracked, the properties of the catalyst, and the technic of contacting the catalyst with the oil.

The cracked efiluent passes through conduit 3 to separation zone 4, which is usually a series of fractionation columns. A light gas fraction is withdrawn through outlet 5. A C4 fraction is passed through conduit 6 to inlet ID. A light gasoline fraction boiling below about 250 F. passes through conduit 1 to storage means 21. A heavy gasoline fraction having a boiling range of about 250 to 400 F. is passed through conduit 9 to alkylation zone II. An aromatic naphtha fraction having a boiling range of about 400 to 500 F. is passed through conduit 8 to treating zone 20. A heavy fraction is recycled through conduit 34.

The heavy gasoline fraction is mixed with isobutane, which enters through inlet I0, and the C4 fraction from conduit 6 and is passed to alkylation zone II. In this zone, the mixture is intimately contacted with concentrated hydrofluoric acid, supplied through inlet I2. Conditions in alkylation zone II are the parafl'ln-olefin alkylation conditions known to the art; for example, the temperature may be about -150 F., the contact time 5-30 minutes, the volume ratio of acid phase to hydrocarbon phase about 1:1, and the isobutane-to-olefin mol ratio about 5:1 to

Sufficient pressure to maintain substantially liquid-phase operation is usually used. Under these conditions, so-called hydrogentransfer alkylation takes place, hydrogen apparently being transferred from the isobutane to the heavy oleflns of the gasoline fraction. The net effects of this reaction are: the heavy olefins become saturated; branched-chain octanes are formed; and someordinary alkylation takes place. Some of the reactions occurring in alkylation zone ll may be exemplified as follows:

H1 1. CmHn C4Hm CroHa C4H| (Decenes) (i-Butane) (Decades) (i-Butene) (i-Butene) (i-Butane) (Branched-chain octanes) HF 3. CnHio 04H nHm (Decenes) (l-Butane) (Tetradecanes) Reaction 3 accounts for a relatively small proportion of the product. It will thus be seen that the liea'v'y oleiins, undesirable in motor gasoline, are converted to the corresponding paraflins. and branched-chain octanes, which are desirable, are produced.

The eiliuent from alkylation zone Ii is passed through conduit II to settling zone 36, in which a hydrocarbon phase is separated from an acid phase. The acid phase may be withdrawn through conduit I4 and passed to regeneration means, not shown; preferably, part is recycled through conduit II. The hydrocarbon phase is passed through conduit It to separation zone H, from which the dissolved hydrogen fluoride is distilled as an azeotropic mixture with light hydrocarbons and recycled through conduit i8 to settling zone 36. Acid-free hydrocarbon material containing organically combined fluorine as a byproduct of the alkylation is passed to treating zone 20.

Treating zone 20 is a system comprising at least three bauxite treaters connected in parallel. The three treaters arediagrarnmatically indicated by A, B, and C. Treater A contains calcined bauxite, which removes organically combined fluorine from the hydrocarbon material entering through conduit l9. Treater B contains bauxite that has been, used for defluorinating the material passing through conduit IS. The material in treater B is used as a catalyst to eil'ect the so-called benzene exchange reaction. The aromatic naphtha from separation zone 4 passes through conduit 8 and is mixed with benzene, supplied through inlet 29. The mixture is reacted in treater B of treating zone 20. Treater C of treating zone 20 contains material that has been used for both the defluorination and the benzene exchange reaction. Super-heated steam is supplied to treater C through inlet 31 to remove fluorine from the bauxite and is withdrawn through outlet 38.

Material passing through conduit I9 is contacted with calcined bauxite in section A at about 100 to 300 F., sufllcient pressure to maintain the hydrocarbon in the liquid phase, and a liquid space velocity of about 1 to 10.

The removal of small proportions of organic fluorine compounds from hydrocarbons by contacting with granular metal oxides has been disclosed and claimed by F. E. Frey in U. S. Patent 2,347,945 (1944). A suitable oxide for this purpose is granular calcined bauxite. The mechanism by which the fluorine removal proceeds is imperfectly understood, but, after contacting with the bauxite under suitable conditions (150-500" F. and liquid space velocities ranging from about 1 to 10 volumes of hydrocarbon per volume of bauxite per hour), the hydrocarbon material is rendered substantially fluorine free (usually less than 0.001 weight per cent F.), the fluorine remaining, in undetermined chemical form, in admixture and/or chemical combination with the bauxite. In commercial practice in which HF- alkylate is defluorinated with bauxite, it has been customary to discard the bauxite when the fluorine content has risen to about to 40 per cent, because, when the fluorine content reaches this range, small amounts of hydrogen fluoride begin to appear in the bauxite-treated hydrocarbon. The present invention utilizes the spent or fluorine-containing bauxite, formerly considered a waste material, to effect another valuable conversion of hydrocarbons, to be described subsequently.

The aromatic naphtha in conduit 8 contains appreciable amounts of polyalkyl aromatics. A two to flve-fold molar excess of benzene is added to this material through inlet 2|, and the mixture is contacted with the fluorine-containing bauxite in treater B at about 800 to 1000 F., pressures up to 600 p. s. i.. and space velocities up to 10 liquid volumes per volume of catalyst per hour. This treatment converts polyalkyl aromatics to monoalkyl aromatics suitable for use in gasoline.

The reaction of high-boiling, polyalkylated aromatics with benzene in the presence of the fluorine-containing bauxite may be exemplified by the following equation;

in which Ar represents an aromatic nucleus and R1 and R: alkyl radicals, which may be identical or difl'erent. This type of reaction is sometimes called the benzene exchange reaction. It will thus be seen that higher-boiling, Polyalkyl aromatics are converted to lower-boiling, monoalkyl aromatics, including monoalkyl benzenes, which are desirable constituents of motor fuels. In processes such as polyforming and cracking, substantial amounts of higher-boiling aromatics are present in recycle fractions higher-boiling than gasoline. The present invention converts such materials to gasoline constituents and utilizes, as a catalyst for this conversion, the fluorine-containing bauxite produced in the defluorination step previously described. A stoichiometric excess of benzene promotes the formation of monoalkyl benzenes. As previously mentioned, a twoto five-fold excess of benzene is ordinarily used. In some cases, however, a smaller proportion of benzene may be used, particularly when polymethyl benzenes are desired.

After the benzene exchange reaction has continued for some time the activity of the catalyst decreases as a result of the deposition of coke and/ or other carbonaceous matter on the catalyst. These deposited materials are removed by the steam treatment subsequently described.

When the material in treater A has been used for a sufllcient length of time so that it contains up to about 20 weight percent or more of fluorine, the material in conduit I! is switched to treater C, in which the bauxite has previously been treated with superheated steam to remove the fluorine. The material in conduit 8 is then switched to treater A, and steam, introduced through conduit 3.1, is switched to treater B. This switching operation is accomplished by suitable manifolding means not shown in the drawing.

The steam treatment or regeneration in treater C is conducted at about 1000 F., as taught by J. D. Gibson in U. S. Patent 2,419,558 (1947'). The regeneration is conducted by passing superheated steam at 600-1000 F. and space velocities equivalent to 0.1 to 5 liquid volumes of water per volume of the spent bauxite per hour. This treatment removes the fluorine, as hydrofluoric acid, from the bauxite and renders the bauxite suitable for further use in the defluorination described. The steam treatment or regeneration also removes the carbonaceous materials deposited on the bauxite during the benzene exchange reaction. It is further advantageous to add air or other oxygen-containing gas to the steam to aid in removing such deposits. The eilluent steam, containing hydrofluoric acid, is withdrawn through outlet 38. The acid may be recovered from the steam, for example by absorption with an alkali-metal fluoride and subsequent desorption, as taught in the Gibson patent cited above.

Thus, in accordance with this invention. the bauxite in a given treater is used in a cyclic series of operations, namely, defluorination. benzene exchange reaction, regeneration with steam, defluorination, benzene exchange, etc.

Defluorinated hydrocarbon material treated in treater A is passed through conduit 2| to separation zone 22. From separation 22, a fraction comprising isobutane is recycled through conduit 23. A fraction boiling in the gasoline range is passed through conduit 24 to storage means 25. A fraction comprising material higher-boiling than gasoline is recycled to cracking zone 2 through conduit 40.

The eiiiuent material from treater B is passed through conduit II to separation zone It. From separation zone 80, a light gas fraction is withdrawn through outlet 32. A fraction comprising unreacted benzene is recycled through conduit 3!. A monoalkyl aromatic fraction is passed through conduit 33 to storage means 25. A fraction boiling above the gasoline range and comprising unreacted polyalkyl aromatics is recycled through conduit 30.

The material in storage means 21 is a lowboiling gasoline fraction comprising oleflns. The material in storage means 25 is a relatively heavy gasoline fraction comprising isoparafllns and aromatics. The materials from these two storage means are blended in desired proportions to form a premium grade gasoline having a high antiknock road rating. This gasoline is withdrawn through outlet 28 as a product of the process. Other hydrocarbons may be added to this product, as desired, to meet volatility specifications.

The invention is not necessarily limited to the specific fractions and boiling ranges mentioned above. For example, the aromatic fraction treated in treater B of zone may be any aromatic fraction boiling between about 300 and 700 F. Refractory recycle stocks obtained in catalytic cracking and in polyforming, as well as in thermal cracking, are suitable. The chief ob- Ject of the treatment by the benzene exchange reaction is to convert relatively high-boiling, polyalkylated aromatics to compounds suitable for use in motor fuel. Non-gasoline materials are thus used to increase yield and quality of gasoline from a given feed.

In another embodiment of the invention, polyalkyl aromatics may be separated from the cracking or polyforming eiiiuent streams by solvent extraction and fractionation before being subjected to the benzene exchange reaction. The benzene for this reaction may be similarly concentrated.

Advantages of this invention are illustrated by the following example. The reactants and their proportions and other specific data are presented as being typical and should not be construed to limit the invention unduly.

A gas oil is cracked over a catalyst comprising alumina and silica at 980 F. and at a space velocity of 1.1 liquid volumes of oil per volume of catalyst per hour. The oil is diluted with steam at a ratio of 60 pounds of steam per barrel of oil. The emuent is treated by conventional methods to remove steam and tar. The resulting hydrocarbon product is fractioned to recover a light gasoline fraction having an end point of about 235 F., a heavy gasoline fraction boiling at 285-400 F" and a heavier recycle stock, which contains an appreciable proportion of aromatics. Part of the recycle stock is fractionated to obtain a fraction boiling at about 400-550" F. T is, fraction is extracted with furfural to obtain an extract, which, after removal of the furfural, comprises an aromatic concentrate boiling at about 4l0530 F.; the raflinate is recycled to the cracking step.

The heavy gasoline fraction is mixed with about 5 volumes of isobutane, and the mixture is contacted with about an equal volume of commercial anhydrous hydrofluoric acid at F. and a contact time of 15 minutes. The eiliuent is freed of acid and normally gaseous hydrocarbons to obtain a liquid alkylate containing about 0.01 weight per cent organically combined fluorine.

The liquid alkylate is contacted with granular bauxite previously calcined at about 700 F. This contacting takes place at 180 F. and a liquid space velocity of about 1. The eilluent alkylate is substantially fluorine-free. It is then fractionated to obtain an alkylate fraction boiling in the motor fuel range and a heavier alkylate fraction. The heavier alkylate is recycled to the cracking step previously described.

After the fluorine content of the bauxite used for the defluorination of the alkylate has risen to about 20 weight per cent, the alkylate stream is switched to a mass of previously used bauxite that has been regenerated by contact with steam and air at 1000 F.

The 410-530 F. aromatic concentrate obtained as described previously is mixed with about 2 volumes of benzene and contacted with the fluorine-containing bauxite at 1000 F., 75 p. s. i., and a liquid space velocity of about 0.9. The product of this step contains about 2 volume per cent of light gas and about 20 volume per cent of an alkyl aromatic fraction boiling in the motor fuel range, the remainder comprising unreacted benzene and apparently unreacted material higher-boiling than motor fuel. About 1.5 weight per cent of the charge to this step is converted to carbon, which is deposited on the fluorinecontaining bauxite catalyst. After the activity of this catalyst has declined to an undesirably low level as a result of carbon deposition, the catalyst is regenerated with steam and air, as previously mentioned, and is then again suitable for defluorinating the liquid alkylate.

The light gasoline fraction from the cracking step, the motor-fuel alkylate, and the alkyl aromatic motor fuel fraction produced by the reaction of the 410-530 F. aromatic concentrate with benzene are blended to obtain a premium gasoline stock. This stock comprises oleiins boiling below 250 F., isoparamns (including branched-chain octanes), and alkyl aromatics. It may be blended with conventional base stocks and stabilized in known manner to obtain finished gasoline.

This invention affords utilization of a spent bauxite defluorination catalyst of any hydrocarbon conversion process employing a catalyst comprising hydrofluoric acid by which catalyst is meant liquid hydrogen fluoride either alone or in mixture with minor amounts of compounds exerting a promoting or modifying effect upon the activity thereof. Such compounds are, for example, boron fluoride or certain metalloid halides,etc.

In one modification, the aromatic product of the benzene exchange reaction may be processed by fractionation and/or solvent extraction to accuse recover individual alkyi aromatics in purified form.

As will be evident to those skilled in the art,

-scope ot the disclosure or from the scope of the claims Iclaim:

1. A process for producing monoalkyl aromatic hydrocarbons which comprises reacting benzene with a polyalkyl aromatic-rich stock in the presence of spent bauxite/defluorinatlon catalyst to term monoalbl aromatic hydrocarbons, and recovering said monoalkyl aromatic hydrocarbons from the total reaction product; said spent-defluorination catalyst having previously been used ior removing organically combined fluorine irom hydrocarbons until having become spent as a result of accumulation of fluorine-containing compounds thereon.

2. A process for producing monoaikyl aromatic hydrocarbons which comprises admixing benzene in molar excess with a polyalkyl aromaticrich stock in a ratio in the range of 2:1 to 5:1, contacting the admixture with spent bauxite defluorinatlon catalyst at a temperature in the range of 800 to 1000 F., at a pressure within the limits or 0 and 600 p. s. i. g. and at a liquid space velocity in the range of 1 to 10; said spent defluorination catalyst comprising bauxite, previously utilized in a hydrocarbon conversion process employing a catalyst comprising hydrofluoric acid to remove from the liquid hydrocarbon conversion eflluent organically combined fluorine present therein and formed as a byproduct of said conversion, said bauxite having been so utilized until spent as a result of accumulation of fluorine containing compounds thereon.

3. A process for the utilization of spent bauxite defluorination catalyst comprising bauxite utilized in a defluorination step of a hydrocarbon conversion process employing a catalyst comprising hydrofluoric acid to remove from liquid hydrocarbon alkylation eifluent organically combined fluorine present therein and formed as a by-product of said alkylation, said bauxite having an accumulation of fluorine compounds thereon, which process comprises eflecting such a defluorination step in a hydrofluoric acid hydrocarbon conversion process in the presence of a first bauxite catalyst until said flrst catalyst becomes spent, reacting benzene with a polyalkyl aromatic-rich stock in the presence of a second bauxite catalyst comprising catalyst spent in such a defluorination step to form monoalkyl aromatic hydrocarbons while concomitantly depositing carbonaceous material on said second catalyst thereby reducing the catalytic activity thereof, in a regeneration step contacting a third bauxite catalyst used previously in such a benzene poLvalkyl aromatic reaction with steam and an oxygen-containing gas so as to remove carbonaceous materials and fluorine compounds de-' posited thereon; when said first catalyst becomes spent diverting the flow oi fluorine-containing hydrocarbon material from said first catalyst to said third catalyst regenerated as aforesaid, diverting the flow oi benzene-polyalkyl aromatic feed from said second catalyst to said flrst catalyst, and in a regeneration step contacting said second catalyst with steam and an oxygencontalning gas to remove carbonaceous material and fluorine compounds deposited thereon.

GEORGE N. CADE.

REFERENCES CITED The following references are of record in the flle 01 this patent:

UNITED STATES PATENTS 

1. A PROCESS FOR PRODUCING MONOALKYL AROMATIC HYDROCARBONS WHICH COMPRISES REACTING BENZENE WITH A POLYALKYL AROMATIC-RICH STOCK IN THE PRESENCE OF SPENT BAUXITE DEFLUORINATION CATALYST TO FORM MONOALKYL AROMATIC HYDROCARBONS, AND RECOVERING SAID MONOALKYL AROMATIC HYDROCARBONS FROM THE TOTAL REACTION PRODUCT; SAID SPENT DEFLUORINATION CATALYST HAVING PREVIOUSLY BEEN USED FOR REMOVING ORGANICALLY COMBINED FLUORINE FROM HYDROCARBONS UNTIL HAVING BECOME SPENT AS A RESULT OF ACCUMULATION OF FLUORINE-CONTAINING COMPOUNDS THEREON. 